Studies on the Brwon Discoloration of Fish Products-I

Factors Affecting the Discoloration

Abstract

During the storage of fish products, the development of brown discoloration is often a serious problem, for the discoloration is usually associated with off flavor and deterioration of nutritional value.
It is generally believed that the discoloration is the reaction of the carbonyl compounds of autoxidized oil and the various amino compounds, but the detailed mechanism is yet not known. In order to ascertain what kind of amino and carbonyl compounds are the major substances in the brown discoloration, the following model experiments were carried out.
The amino compounds separated from boiled-dried anchovy, dried mackerel, and salted trout were divided into volatile and non-volatile fractions by steam distillation (Fig. 1), and these are shaken with both the autoxidizied methyl linoleate and the methyl ester or cuttlefish liver oil at 40°C for 4 hours. The colored ether-soluble fraction was dissolved in ethanol and the optical density at 430mμ was measured.
As a result, though the reaction of the non-volatile fraction was negligible, the volatile fraction discolorated remarkably. This suggested that in the development of brown discoloration the action of the volatile fraction such as ammonia and trimethylamine is superior to that of the non-volatile fraction including amino acids (Table 2). The volatile amino compounds from 5g of dried mackerel reacted maximumly with 0.5g of the autoxidized methyl ester of cuttle-fish liver oil (Fig. 3).
During the development of discoloration the amount of unsaturated carbonyl compounds decreased, while, the decrease of saturated carbonyl compounds was limited (Fig. 5). This result indicated that the role of unsaturated carbonyls in the discoloration reaction seems more important than that of saturated.